1. Field
The present disclosure relates generally to integrated circuits, and more particularly, to read/write assists for memory.
2. Background
Integrated circuits (or “chips”) have revolutionized the electronic industry by enabling complex circuits consisting of millions of transistors, diodes, resistors and capacitors to be integrated into a chip of semiconductor material. Integration also provides other benefits such as batch manufacturing. The simultaneous manufacture of hundreds or even thousands of integrated circuits onto a single semiconductor wafer reduces cost and increases reliability of the end products.
Despite the manufacturing benefits of integrated circuits, process variations during the manufacturing process can have an impact on the electrical parameters of the chips, thereby leading to variations in performance. Statistically, most of the chips manufactured on a semiconductor wafer will have electrical parameters that meet the nominal specifications. A number of chips, however, will deviate from the nominal case towards the process corners. By way of example, a number of CMOS chips manufactured from a wafer may have both their PMOS and NMOS transistors operating at either a slow corner (SS) or a fast corner (FF). Other CMOS chips manufactured from the same wafer may have their transistors operating at cross corners where one type of transistor is faster and the other type of transistor is slower. By way of example, some CMOS chips may have a slow-fast (SF) corner with slow NMOS transistors and a fast PMOS transistors. Other CMOS chips may have a fast-slow corner (FS) with fast NMOS transistors and slow PMOS transistors.
Memory is a common circuit implemented within an integrated circuit. A static random access memory (SRAM) is just one example. The SRAM is memory that requires power to retain data. Unlike dynamic random access memory (DRAM), the SRAM does not need to be periodically refreshed. The SRAM also provides faster access to data than DRAM making it an attractive choice for many integrated circuit applications. Unfortunately, chips operating at the SF corner tend to have difficulty writing to SRAM and chips operating at the FS corner tend to have difficulty reading from SRAM.
Different read and write assist techniques have been used in the past. However, these techniques are often costly in terms of chip area and power consumption. Accordingly, there is a need in the art for new techniques and methods that provide read and write assist to memory and other circuits that occupy less chip areas and consume less power.